1. Field of the Invention
The invention generally relates to a system and related methods that utilize one or more nozzles for irradiating substrates using a gas cluster ion beam (GCIB), and more particularly to systems and related methods capable or rapidly changing between different supplies of gas to the one or more nozzles.
2. Description of Related Art
Gas cluster ion beams (GCIB's) are used for doping, etching, cleaning, smoothing, and growing or depositing layers on a substrate. For purposes of this discussion, gas clusters are nano-sized aggregates of materials that are gaseous under conditions of standard temperature and pressure. Such gas clusters may consist of aggregates including a few to several thousand molecules, or more, that are loosely bound together. The gas clusters can be ionized by electron bombardment, which permits the gas clusters to be formed into directed beams of controllable energy. Such cluster ions each typically carry positive charges given by the product of the magnitude of the electronic charge and an integer greater than or equal to one that represents the charge state of the cluster ion. The larger sized cluster ions are often the most useful because of their ability to carry substantial energy per cluster ion, while yet having only modest energy per individual molecule. The ion clusters disintegrate on impact with the substrate. Each individual molecule in a particular disintegrated ion cluster carries only a small fraction of the total cluster energy. Consequently, the impact effects of large ion clusters are substantial, but are limited to a very shallow surface region. This makes gas cluster ions effective for a variety of surface modification processes, but without the tendency to produce deeper sub-surface damage that is characteristic of conventional ion beam processing.
Conventional GCIB systems produce beams of clusters from a variety of gases, such as helium, neon, argon, krypton, xenon, nitrogen, oxygen, carbon dioxide, sulfur hexafluoride, nitric oxide, nitrous oxide, and mixtures of these gases. Several emerging applications for GCIB processing of substrates on an industrial scale are in the semiconductor field. Although GCIB processing of a substrate is performed using a wide variety of gas cluster source gases, many of which are inert gases, many semiconductor processing applications use reactive source gases, sometimes in combination or mixture with inert or noble gases, to form the GCIB. Certain gas or gas mixture combinations are incompatible with one another due to their reactivity. Moreover, GCIB processes sometimes involve changing the supply of gas to one or more nozzles emitting the gas cluster beams. In order to provide for such changes between supplies of gas, it is sometimes necessary to substantially evacuate one gas from all gas-holding volumes immediately upstream of the one or more nozzles before a second, incompatible gas can be supplied to the one or more nozzles. A need therefore exists for GCIB systems and related methods capable of changing the supply of gas between different supplies as rapidly as possible, to thereby minimize downtime associated with such changes.